Method for polymerization of olefin

ABSTRACT

The present invention is directed to a method for polymerizing olefins in a multi-stage polymerization apparatus including a gas-phase polymerization reactor in a subsequent stage. By use of the present method, the composition of gas in the gas-phase reactor is easily adjusted, and moreover, a polymer having an intended composition is produced in a consistent manner. In one aspect, the method for polymerizing olefins is performed in successive, multiple stages by use of a plurality of polymerization reactors disposed in series which include at least one gas-phase polymerization reactor after a first reactor, wherein a multi-component gas is removed from a gas-phase reactor and pressurized and/or cooled to thereby liquefy a portion of the gas; at least a portion of gas is discharged; and the remaining gas and the liquid are returned to the gas-phase reactor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for polymerizingolefins such as ethylene and propylene, and more particularly to amethod for polymerizing olefins in a multi-stage polymerizationapparatus comprising a gas-phase polymerization reactor in which thecomposition of gas is easily controlled.

[0003] 2. Background Art

[0004] Among a variety of industrial methods for polymerizing olefinssuch as ethylene and propylene, a gas-phase polymerization method hasbecome of interest. This method utilizes high-activity catalyst and doesnot require a deashing (removal of catalyst residue) process.

[0005] However, in the case of a successive multi-stage gas-phasepolymerization method, the composition of gas in a polymerizationreactor of a certain stage affects the composition of gas in apolymerization reactor of a subsequent stage. Therefore, adjustment ofthe composition of gas in the reactor of a subsequent stage may bedifficult.

[0006] For example, in order to produce a polymer having a broadmolecular weight distribution, usually a low molecular weight polymer isproduced in a reactor of a certain stage, and in a reactor of asubsequent stage the resultant polymer is further polymerized to yield ahigher polymer. In this case, in the preceding polymerization, hydrogengas of high concentration is used as a chain-transfer agent. However,since hydrogen gas of low concentration is used in the subsequentpolymerization, when the polymer is transferred from a preceding reactorto a subsequent reactor there must be removed a large amount of hydrogengas accompanying a produced polymer.

[0007] In addition, when a copolymer such as ethylene-propylene is to beproduced, the composition of gas in each polymerization reactor must beadjusted.

[0008] Therefore, several methods have been proposed for adjusting thecomposition of gas in a gas-phase polymerization reactor of a subsequentstage. Japanese Patent Application Laid-Open (kokai) No. 23001/1984discloses a method in which a purge vessel is provided between twosequential polymerization reactors for adjusting the concentration ofhydrogen gas (a chain-transfer agent) contained in an accompanying gasincluding a polymer fed from a preceding polymerization reactor, whereinthe accompanying gas is removed and only the polymer is transferred to asubsequent reactor. Also, Japanese Patent Application Laid-Open (kokai)No. 65703/1982 discloses a method in which an accompanying gascontaining a polymer is diluted with inert gas in a purge vessel, tothereby transfer to a subsequent reactor the polymer accompanied byhydrogen gas of low concentration. Furthermore, Japanese PatentApplication Laid-Open (kokai) No. 118342/1995 discloses a method inwhich a purge vessel is formed of a tank for gas and a tank for powder,and an accompanying gas containing a polymer is removed by operation ofa valve between the two tanks, and then the polymer in the tank forpowder is transferred to a subsequent polymerization reactor by use ofpressurized circulating gas from the subsequent reactor. However, thesemethods still have drawbacks, such as requirement of a purge vessel andcomplicated valve control operation.

SUMMARY OF THE INVENTION

[0009] The present inventors have performed extensive studies in anattempt to solve the above-described drawbacks, and have found that itis possible to adjust the composition of gas and to control temperature,i.e., removal of heat of polymerization, in a gas-phase polymerizationreactor by removing gas from a subsequent gas-phase polymerizationreactor; pressurizing and cooling the gas to partially liquefy the gas;discharging at least a portion of the gas; and returning the remaininggas and the liquid to the reactor. Based on this finding, the inventorshave accomplished the present invention.

[0010] Accordingly, an object of the present invention is to provide amethod for polymerizing olefins in a multi-stage polymerizationapparatus comprising a gas-phase polymerization reactor in a subsequentstage, wherein the composition of gas in the gas-phase reactor is easilyadjusted, and whereby a polymer having an intended composition isproduced in a continuous process.

[0011] In a first aspect of the present invention, there is provided amethod for polymerizing olefins in successive, multiple stages by use ofa plurality of polymerization reactors disposed in series comprising atleast one gas-phase polymerization reactor after a first reactor,wherein a multi-component gas is removed from a gas-phase reactor andpressurized and/or cooled to thereby liquefy a portion of the gas; atleast a portion of the removed gas is discharged; and the remaining gasand the liquid are returned to the gas-phase reactor.

[0012] In a second aspect of the present invention, there is provided amethod for polymerizing olefins in successive multi-stages by use of aplurality of polymerization reactors disposed in series comprising atleast one gas-phase polymerization reactor after a first reactor,wherein a multi-component gas is removed from a gas-phase reactor andpressurized and/or cooled to thereby liquefy a portion of the gas; theliquid is returned to the gas-phase reactor; the remaining gas isfurther pressurized and/or cooled to thereby liquefy a portion of thegas; at least a portion of the gas is discharged; and the remaining gasand the liquid are returned to the gas-phase reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a process flowchart showing one example according to thepresent invention, in which light gas is separated from amulti-component gas in a polymerization reactor in a single stage; and

[0014]FIG. 2 is a process flowchart showing an example of the presentinvention, in which light gas is separated from a multi-component gas ina polymerization reactor in two stages.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Modes of the present invention will next be described.

A. Method of Successive Multi-Stage Polymerization Covered by the Scopeof the Invention

[0016] The method for polymerizing olefins of the present invention isapplied to homopolymerization or copolymerization of olefins such asethylene, propylene, butene-1, pentene-1, hexene-1, octene-1, and4-methylpentene-1. Also, the method is applied to copolymerizationbetween olefins and another monomer.

[0017] In the method for polymerizing olefins of the present invention,polymerization catalysts are typically used. For example, among alltypes of catalysts used for polymerization of olefins, a customaryZiegler solid catalyst is preferably used.

[0018] A typical Ziegler solid catalyst comprises a titanium compound,an organoaluminum compound, and an electron donor. Examples of thetitanium compound include titanium halides such as titaniumtetrachloride, titanium tetrabromide, and titanium tetraiodide. Examplesof the organoaluminum compound include alkylaluminums such astrimethylaluminum and triethylaluminum. Examples of the electron donorinclude organosilane compounds such as tetraethoxysilane,diphenyldimethoxysilane, and dicyclopentyldimethoxysilane. In thepresent invention, the electron donor is used in order to adjust thestereoregularity, the molecular weight, and the molecular weightdistribution of a polymer.

[0019] The present invention provides a method of successive multi-stagepolymerization by use of a plurality of polymerization reactors (usuallyabout 2-10 reactors) disposed in series and comprising at least onegas-phase polymerization reactor after the first reactor. In otherwords, a polymerization apparatus comprising gas-phase polymerizationreactor in multiple stages, or a polymerization apparatus comprising acombination of gas-phase and liquid-phase polymerization reactors inmultiple stages is satisfactory for carrying out the polymerizationmethod of the present invention, so long as at least one reactor afterthe first reactor is a gas-phase polymerization reactor.

[0020] As used herein, the term “gas-phase polymerization reactor”refers generally to a polymerization reactor for allowing polymerizationof a monomer gas containing a catalyst in gas phase, wherein a producedpolymer and a monomer coexist. Various types of gas-phase polymerizationreactors are available, and typical examples thereof include anagitation-type gas-phase polymerization reactor and a fluidized bedgas-phase polymerization reactor.

[0021] The term “liquid-phase polymerization reactor” refers generallyto a polymerization reactor for allowing polymerization of a monomer inliquid phase, wherein a monomer is liquefied solely or with a solvent(e.g. paraffin such as n-heptane or hexane), and wherein a preliminarypolymerized polymer containing a catalyst exists in slurry form in aliquid phase. Available types of liquid-phase polymerization reactorsinclude a loop-type bulk polymerization reactor and an agitation-typeslurry polymerization reactor.

[0022] In a polymerization apparatus in which gas-phase and liquid-phasepolymerization reactors are used in combination, the two types ofreactors differ in terms of the phases of materials contained therein,and a vaporizing apparatus or a liquefying apparatus must be providedbetween a gas-phase polymerization reactor and a liquid-phasepolymerization reactor in order to perform phase conversion.

[0023] Examples of the sequence of polymerization reactors employed inthe method of polymerization of the present invention are describedbelow for the cases of two-stage, three-stage, and four-or-more-stagepolymerization. As used herein, “gas” refers to a gas-phasepolymerization reactor, and “liquid” refers to a liquid-phasepolymerization reactor, and “-” refers to a connection between reactors.

[0024] (1) Two-stage polymerization

[0025] gas-gas, liquid-gas

[0026] (2) Three-stage polymerization

[0027] gas-gas-gas, liquid-gas-gas, gas-liquid-gas, liquid-liquid-gas,gas-gas-liquid, liquid-gas-liquid

[0028] (3) Four-or-more-stage polymerization

[0029] A sequence for a four-or-more-stage polymerization is obtained byattaching “gas” or “liquid” to the last stage of a sequence forpolymerization 1 order lower. For example, in the case of four-stagepolymerization, “gas” or “liquid” is attached to the last stage of asequence listed above for three-stage polymerization, and in the case ofseven-stage polymerization, “gas” or “liquid” is attached to the laststage of a sequence employed for six-stage polymerization.

B. Method for Adjusting the Composition of Gas in a Gas-PhasePolymerization Reactor

[0030] As described above, the present invention is directed to a methodof performing successive multi-stage polymerization of olefins by use ofa plurality of polymerization reactors disposed in series and comprisingat least one gas-phase polymerization reactor after the first reactor.In a gas-phase polymerization reactor, the composition of gas must beadjusted in order to adjust the molecular weight distribution of apolymer and to control the polymerization proportions of a plurality ofmonomers and the molecular weight of a polymer. The present inventionprovides a method for adjusting the composition of gas easily in agas-phase polymerization reactor, even when the composition of gas fromthe preceding polymerization reactor is not preferable for the gas-phasereactor.

[0031] The present invention provides a method for adjusting thecomposition of gas in a gas-phase polymerization reactor, wherein gas isremoved from the reactor and the gas is pressurized and/or cooled toliquefy a portion of the gas(mainly heavy gas components), to therebyisolate light gas, and at least a portion of the light gas isdischarged. More specifically, the present invention provides a methodfor isolating light gas in a single stage and a method for isolatinglight gas in two stages.

[0032] (1) Method for isolating, in a single stage, light gas from thegas in a polymerization reactor

[0033] The first aspect of the present invention is directed to a methodof successive multi-stage polymerization of olefins by use of aplurality of polymerization reactors arranged in series and comprisingat least one gas-phase polymerization reactor after the first reactor,wherein a multi-component gas is removed from the gas-phasepolymerization reactor and is pressurized and/or cooled, to therebyliquefy a portion of the gas, and subsequently a portion of the gas isdischarged and the remaining gas and the liquid are returned to thereactor.

[0034] In the present invention, when a gas removed from a gas-phasepolymerization reactor is a multi-component gas, it means that the gascontains multi-component monomers, or a monomer and hydrogen whichserves as a chain-transfer agent. When the multi-component gas isliquefied, a heavier gas component is preferentially liquefied, andlight gas components are included in the remaining gas at high content.Therefore, the gas in the polymerization reactor can be made to containheavier components as a result of a portion of the remaining gas beingdischarged and another portion of the remaining gas and the liquid beingreturned to the reactor. Hereinafter, light gas components may becollectively referred to as light gas, and similarly, heavy gascomponents may be collectively referred to as heavy gas.

[0035] Regardless of the type of reactor; i.e., an agitation-typegas-phase polymerization reactor or a fluidized bed polymerizationreactor, gas is preferably removed from the upper portion of thereactor, because in the reactor, gas is usually present in upper 20-30%of the volume of the reactor and polymerized powder in a lower portion.

[0036] Gas removed from a gas-phase polymerization reactor is liquefiedpartially, and subsequently the liquid is returned to the reactor andvaporized therein. Therefore, the latent heat of vaporization may beused for removal of the heat of reaction generated in the reactor. Thus,the present invention enables adjustment of the composition of gas inthe reactor and control of reactor temperature.

[0037] The present invention is specifically described by reference toFIG. 1 showing a process flow.

[0038] In FIG. 1, the terms “first polymerization reactor” and “secondpolymerization reactor” respectively refer to the first and the secondpolymerization reactors among a plurality of polymerization reactorsdisposed in series, and in the case of neighboring reactors these termsrefer to a preceding reactor and a subsequent reactor. For the sake ofsimplicity, the following description will be given of the case in whichboth a first polymerization reactor and a second polymerization reactorserve as gas-phase polymerization reactors.

[0039] Propylene (1), a catalyst (2), hydrogen (3) an organoaluminumcompound (4), and an electron donor (5) are supplied to a firstpolymerization reactor (6), and propylene is subjected tohomopolymerization. Subsequently, the polymerized powder and theaccompanying gas are supplied to a second polymerization reactor (8)through a powder transfer line (7), and copolymerization ofpropylene-ethylene is subsequently performed in the second reactor (8).The powder produced in the second reactor (8) and the accompanying gasare removed from the reactor through a powder transfer line (9).Circulation gas (10), which is used in the second reactor (8) forcooling, is pressurized by use of a compressor (12) and cooled in afirst heat exchanger (13), to thereby obtain a gas-liquid mixed-phasefluid. In a first separator (15), light gas is isolated from thegas-liquid mixed-phase fluid and discharged through a gas discharge line(14). Subsequently, the remaining component (first separator liquid(16)) is transferred to the second reactor (8) in order to remove theheat of reaction generated therein. Ethylene (17) and propylene (18),which are necessary for producing a copolymer in the secondpolymerization reactor (8), are supplied to the first separator liquid(16).

[0040] (2) Method of isolating, in two stages, light gas from the gas ina polymerization reactor

[0041] The present invention is directed to a method of successivemulti-stage polymerization of olefins by use of a plurality ofpolymerization reactors arranged in series and comprising at least onegas-phase polymerization reactor after the first reactor, wherein amulti-component gas is removed from the gas-phase polymerization reactorand pressurized and/or cooled, to thereby liquefy a portion of the gas,and subsequently the liquid is returned to the reactor and the remaininggas is further pressurized and/or cooled, to thereby liquefy a portionthereof, and at least a portion of the gas is discharged and theremaining gas and the liquid are returned to the reactor.

[0042] The method according to the second aspect of the invention isbasically identical with that of the first aspect, but in the method ofthe second aspect, light gas is isolated in two stages from the gascontained in a polymerization reactor.

[0043] In other words, the second aspect of the present invention isdirected to a method for discharging light gas at high performance,i.e., the content of light gas components is high in a discharged gas.This method is most practical, since it enables continuous operation byuse of a few pieces of fixed equipment. Therefore, in order to moreefficiently isolate light gas from a gas-liquid mixed-phase fluid, inaccordance with needs there is employed three- or four-stage isolation,or a method for higher order isolation by use of a distillation column.

[0044] This mode of the present invention is specifically described byreference to FIG. 2, which shows a process flow.

[0045] Propylene (1), a catalyst (2), hydrogen (3) an organoaluminumcompound (4), and an electron donor (5) are supplied to a firstpolymerization reactor (6), and the propylene is subjected tohomopolymerization. Subsequently, the polymerized powder and anaccompanying gas are supplied to a second polymerization reactor (8)through a powder transfer line (7), and copolymerization ofpropylene-ethylene is subsequently performed in the second reactor (8).The powder produced in the second reactor (8) and an accompanying gasare removed from the reactor through a powder transfer line (9).Circulation gas (10), which is used in the second reactor (8) forcooling, is pressurized by use of a compressor (12) and cooled in afirst heat exchanger (13), to thereby obtain a gas-liquid mixed-phasefluid. In a first separator (15), gas (gas from a first separator (19))is isolated from the gas-liquid mixed-phase fluid, and the remainingcomponent (first separator liquid (16)) is returned to the secondreactor in order to remove the heat of reaction generated therein. Gasfrom a first separator (19) is further cooled in a second heat exchanger(20), to thereby obtain a gas-liquid mixed phase fluid. In a secondseparator (21), gas is isolated from the gas-liquid mixed phase fluidand discharged through a gas discharge line (14). Subsequently, theremaining component (second separator liquid (22)) is returned to thesecond reactor (8) in order to remove the heat of reaction generatedtherein. Ethylene (17) and propylene (18), which are necessary forproducing a copolymer in the second polymerization reactor (8), aresupplied to the second separator liquid (22).

C. Application Examples of the Present Invention

[0046] Application examples of the method for polymerizing olefins ofthe present invention are described below.

[0047] 1) Applications of two-stage polymerization

[0048] Case 1. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor, and a propylenehomopolymer having a high molecular weight is produced in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line, wherein the concentration of hydrogen in the componentis higher than that in a gas component contained in the secondpolymerization reactor.

[0049] Case 2. An ethylene homopolymer having a low molecular weight isproduced in the first polymerization reactor, and an ethylenehomopolymer having a high molecular weight is produced in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line, wherein the concentration of hydrogen in the componentis higher than that in a gas component contained in the secondpolymerization reactor.

[0050] Case 3. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor, and a propylene-ethylenecopolymer having a high molecular weight is produced in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line, wherein the concentration of hydrogen in the componentis higher than that in a gas component contained in the secondpolymerization reactor.

[0051] Case 4. An ethylene homopolymer having a low molecular weight isproduced in the first polymerization reactor, and a propylene-ethylenecopolymer having a high molecular weight is produced in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line, wherein the concentration of hydrogen in the componentis higher than that in a gas component contained in the secondpolymerization reactor.

[0052] Case 5. A propylene homopolymer is produced in the firstpolymerization reactor, and a propylene-1-butene copolymer is producedin the second polymerization reactor. A gas component is dischargedthrough a gas discharge line, wherein the concentration of propylene inthe component is higher than that in a gas component contained in thesecond polymerization reactor.

[0053] Case 6. An ethylene homopolymer is produced in the firstpolymerization reactor, and an ethylene-propylene copolymer is producedin the second polymerization reactor. A gas component is dischargedthrough a gas discharge line, wherein the concentration of ethylene inthe component is higher than that in a gas component contained in thesecond polymerization reactor.

[0054] Case 7. An ethylene homopolymer is produced in the firstpolymerization reactor, and an ethylene-1-hexene copolymer is producedin the second polymerization reactor. A gas component is dischargedthrough a gas discharge line, wherein the concentration of ethylene inthe component is higher than that in a gas component contained in thesecond polymerization reactor.

[0055] Case 8. An ethylene-propylene copolymer having a low molecularweight is produced in the first polymerization reactor, and anethylene-propylene copolymer having a high molecular weight is producedin the second polymerization reactor. A gas component is dischargedthrough a gas discharge line, wherein the concentration of hydrogen inthe component is higher than that in a gas component contained in thesecond polymerization reactor.

[0056] Case 9. An ethylene-propylene copolymer is produced in the firstpolymerization reactor, and in the second reactor there is produced anethylene-propylene copolymer having a higher content of propylene ascompared with the copolymer produced in the first polymerizationreactor. A gas component is discharged through a gas discharge line,wherein the concentration of ethylene in the component is higher thanthat in a gas component contained in the second polymerization reactor.

[0057] These methods are applied to the case where the gas and/or theliquid accompanying a polymer produced in the first polymerizationreactor are supplied to the second polymerization reactor, wherein arelatively light component in the second reactor is supplied to thesecond reactor excessively.

[0058] 2) Applications of three-stage polymerization

[0059] Case 1. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; a propylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and a propylene homopolymer having a higher molecular weight ascompared with the homopolymer produced in the second reactor is producedin the third polymerization reactor. A gas component is dischargedthrough a gas discharge line of a circulation system of the secondpolymerization reactor, wherein the concentration of hydrogen in thecomponent is higher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0060] Case 2. An ethylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; an ethylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and an ethylene homopolymer of higher molecular weight ascompared with the homopolymer produced in the second reactor is producedin the third polymerization reactor. A gas component is dischargedthrough a gas discharge line of a circulation system of the secondpolymerization reactor, wherein the concentration of hydrogen in thecomponent is higher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0061] Case 3. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; a propylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and an ethylene-propylene copolymer is produced in the thirdpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the second polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0062] Case 4. An ethylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; an ethylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and an ethylene-propylene copolymer is produced in the thirdpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the second polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of ethylene in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0063] Case 5. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; a propylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and a propylene-1-butene copolymer is produced in the thirdpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the second polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of propylene in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0064] Case 6. A propylene homopolymer having a low molecular weight isproduced in the first polymerization reactor; a propylene homopolymerhaving a high molecular weight is produced in the second polymerizationreactor; and a propylene-1-butene copolymer is produced in the thirdpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the second polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the secondpolymerization reactor. A gas component is discharged through a gasdischarge line of a circulation system of the third polymerizationreactor, wherein the concentration of hydrogen in the component ishigher than that in a gas component contained in the thirdpolymerization reactor.

[0065] Case 7. A propylene homopolymer is produced in the firstpolymerization reactor; an ethylene-propylene copolymer is produced inthe second polymerization reactor; and an ethylene-propylene copolymerhaving a higher content of propylene as compared with the copolymerproduced in the second reactor is produced in the third polymerizationreactor. A gas component is discharged through a gas discharge line of acirculation system of the second polymerization reactor, wherein theconcentration of hydrogen in the component is higher than that in a gascomponent contained in the second polymerization reactor. A gascomponent is discharged through a gas discharge line of a circulationsystem of the third polymerization reactor, wherein the concentration ofethylene in the component is higher than that in a gas componentcontained in the third polymerization reactor.

[0066] Case 8. An ethylene homopolymer is produced in the firstpolymerization reactor; an ethylene-propylene copolymer is produced inthe second polymerization reactor; and an ethylene-propylene copolymerhaving a higher content of propylene as compared with the copolymerproduced in the second reactor is produced in the third polymerizationreactor. A gas component is discharged through a gas discharge line of acirculation system of the second polymerization reactor, wherein theconcentration of hydrogen in the component is higher than that in a gascomponent contained in the second polymerization reactor. A gascomponent is discharged through a gas discharge line of a circulationsystem of the third polymerization reactor, wherein the concentration ofethylene in the component is higher than that in a gas componentcontained in the third polymerization reactor.

[0067] Case 9. An ethylene homopolymer is produced in the firstpolymerization reactor; an ethylene-propylene copolymer is produced inthe second polymerization reactor; and an ethylene-propylene copolymerhaving a higher content of propylene as compared with the copolymerproduced in the second reactor is produced in the third polymerizationreactor. A gas component is discharged through a gas discharge line of acirculation system of the second polymerization reactor, wherein theconcentration of ethylene in the component is higher than that in a gascomponent contained in the second polymerization reactor. A gascomponent is discharged through a gas discharge line of a circulationsystem of the third polymerization reactor, wherein the concentration ofethylene in the component is higher than that in a gas componentcontained in the third polymerization reactor.

[0068] Case 10. An ethylene homopolymer is produced in the firstpolymerization reactor; an ethylene-1-hexene copolymer is produced inthe second polymerization reactor; and an ethylene-1-hexene copolymerhaving a higher content of 1-hexene as compared with the copolymerproduced in the second reactor is produced in the third polymerizationreactor. A gas component is discharged through a gas discharge line of acirculation system of the second polymerization reactor, wherein theconcentration of hydrogen in the component is higher than that in a gascomponent contained in the second polymerization reactor. A gascomponent is discharged through a gas discharge line of a circulationsystem of the third polymerization reactor, wherein the concentration ofethylene in the component is higher than that in a gas componentcontained in the third polymerization reactor.

[0069] Case 11. An ethylene homopolymer is produced in the firstpolymerization reactor; an ethylene-1-hexene copolymer is produced inthe second polymerization reactor; and an ethylene-1-hexene copolymerhaving a higher content of 1-hexene as compared with the copolymerproduced in the second reactor is produced in the third polymerizationreactor. A gas component is discharged through a gas discharge line of acirculation system of the second polymerization reactor, wherein theconcentration of ethylene in the component is higher than that in a gascomponent contained in the second polymerization reactor. A gascomponent is discharged through a gas discharge line of a circulationsystem of the third polymerization reactor, wherein the concentration ofethylene in the component is higher than that in a gas componentcontained in the third polymerization reactor.

[0070] These methods are applied to the case where the gas and/or theliquid accompanying a polymer produced in the first polymerizationreactor are supplied to the second polymerization reactor, wherein arelatively light component of the gas and/or the liquid in the secondreactor are supplied to the second reactor excessively, and furthermore,the gas and/or the liquid accompanying a polymer produced in the secondpolymerization reactor are supplied to the third polymerization reactor,wherein a relatively light component of the gas and/or the liquid in thethird reactor are supplied to the third reactor excessively.

EXAMPLES

[0071] The present invention will next be described in more detail byway of examples.

Example 1

[0072] In an apparatus as shown in FIG. 1, a propylene homopolymerhaving a low molecular weight was produced in a first polymerizationreactor (6), and a propylene-ethylene copolymer having a high molecularweight was produced in a second polymerization reactor (8), to therebyobtain a propylene-ethylene copolymer having a high limiting viscosity(η) corresponding to the copolymerization portion. In this apparatus,polymerization reactors (volume: 200 liters) were used. Atitanium-tetrachloride-on-magnesium catalyst was supplied to a firstpolymerization reactor (6) through a catalyst supply line (2) at a rateof about 0.04 g (as reduced to titanium)/hr, and also, propylene wassupplied to the first reactor (6) at a rate of 37.5 kg/hr.Triethylaluminum serving as an organoaluminum compound catalyst anddicyclopentyldimethoxysilane serving as an electron donor catalyst weresupplied to the first reactor (6) through catalyst supply lines (4) and(5), respectively. When these catalysts were supplied, the mol ratio oftriethylaluminum to dicyclopentyldimethoxysilane was 4:1. In addition,hydrogen gas serving as a chain-transfer agent was supplied to the firstreactor (6) through a supply line (3) at a rate of 1800 liters/hr.

[0073] In the first polymerization reactor (6), polymerization wasperformed at 30 kg/cm².G and 80° C. The produced polymer powder and theaccompanying gas were transferred to a second polymerization reactor (8)through a transfer line (7). In the second reactor (8), polymerizationwas performed at 16.0 kg/cm².G and 60° C. In order to produce acopolymer, ethylene was supplied to the second reactor (8) at a rate of5.1 kg/hr without supply of catalysts. By use of a compressor (12), thepressure of a circulation gas was raised up to 19.7 kg/cm².G. A firstheat exchanger (13) was controlled so as to adjust the temperature in afirst separator (15) to −20° C., and gas was discharged through a gasdischarge line (14) at a rate of 1.02 kg/hr. In the first polymerizationreactor, the mole fraction of hydrogen was 8.9%, and in the secondpolymerization reactor, the mole fractions of hydrogen and ethylene were2.0% and 40.1%, respectively. Through this two-stage polymerization, inthe second polymerization reactor a propylene-ethylene copolymercontaining 45% ethylene in the copolymerization portion was produced ata rate of 35.3 kg/hr. In the produced copolymer, limiting viscosity (η)of the homopolymerization portion was 1.1 dl/g and that of thecopolymerization portion was 4.5 dl/g.

[0074] The results are shown in Table 1.

[0075] Herein, limiting viscosity (η: dl/g) was measured in decalin at135° C.

Example 2

[0076] In an apparatus as shown in FIG. 2, a propylene homopolymerhaving a low molecular weight was produced in a first polymerizationreactor (6), and a propylene-ethylene copolymer having a high molecularweight was produced in a second polymerization reactor (8), to therebyobtain a propylene-ethylene copolymer having a high limiting viscosity(η) corresponding to the copolymerization portion. As shown in FIG. 2,polymerization reactors (volume: 200 liters) were used. A titaniumtetrachloride-on-magnesium catalyst was supplied to a firstpolymerization reactor (6) through a catalyst supply line (2) at a rateof about 0.04 g (as reduced to titanium)/hr, and also, propylene wassupplied to the first reactor (6) at a rate of 37.5 kg/hr.Triethylaluminum serving as an organoaluminum compound catalyst anddicyclopentyldimethoxysilane serving as an electron donor catalyst weresupplied to the first reactor (6) through catalyst supply lines (4) and(5), respectively. When these catalysts were supplied, the mol ratio oftriethylaluminum to dicyclopentyldimethoxysilane was 4:1. In addition,hydrogen gas serving as a chain-transfer agent was supplied to the firstreactor (6) through a supply line (3) at a rate of 1800 liters/hr.

[0077] In the first polymerization reactor (6), polymerization wasperformed at 30 kg/cm².G and 80° C. The produced polymer powder and theaccompanying gas were transferred to a second polymerization reactor (8)through a transfer line (7). In the second reactor (8), polymerizationwas performed at 16.0 kg/cm².G and 60° C. In order to produce acopolymer, ethylene was supplied to the second reactor (8) at a rate of8.0 kg/hr without supply of catalysts. By use of a compressor (12), thepressure of a circulation gas was raised up to 19.7 kg/cm².G. A firstheat exchanger (13) was controlled so as to adjust the temperature in afirst separator (15) to 10° C., and a second heat exchanger (20) wascontrolled so as to adjust the temperature in a second separator (21) to−10° C. Gas was discharged through a gas discharge line (14) at a rateof 5.74 kg/hr. In the first polymerization reactor (6), the molefraction of hydrogen was 9.0%, and in the second polymerization reactor(8), the mole fractions of hydrogen and ethylene were 1.3% and 40.0%,respectively. Through this two-stage polymerization, in the secondpolymerization reactor a propylene-ethylene copolymer containing 45%ethylene in the copolymerization portion was produced at a rate of 35.5kg/hr. In the produced copolymer, limiting viscosity (η) of thehomopolymerization portion was 1.1 dl/g and that of the copolymerizationportion was 5.1 dl/g.

[0078] The results are shown in Table 1.

Comparative Example 1

[0079] In an apparatus as shown in FIG. 1, a propylene homopolymerhaving a low molecular weight was produced in a first polymerizationreactor (6), and a propylene-ethylene copolymer having a high molecularweight was produced in a second polymerization reactor (8), to therebyobtain a propylene-ethylene copolymer having a high limiting viscosity(η) corresponding to the copolymerization portion. As shown in FIG. 1,polymerization reactors (volume: 200 liters) were used. A titaniumtetrachloride-on-magnesium catalyst was supplied to the firstpolymerization reactor (6) through a catalyst supply line (2) at a rateof about 0.04 g (as reduced to titanium)/hr, and also, propylene wassupplied to the first reactor (6) at a rate of 37.5 kg/hr.

[0080] Triethylaluminum serving as an organoaluminum compound catalystand dicyclopentyldimethoxysilane serving as an electron donor catalystwere supplied to the first reactor (6) through the catalyst supply lines(4) and (5), respectively. When these catalysts were supplied, the molratio of triethylaluminum to dicyclopentyldimethoxysilane was 4:1. Inaddition, hydrogen gas serving as a chain-transfer agent was supplied tothe first reactor (6) through a supply line (3) at a rate of 1800liters/hr.

[0081] In the first polymerization reactor (6), polymerization wasperformed at 30 kg/cm².G and 80° C. The produced polymer powder and theaccompanying gas were transferred to the second polymerization reactor(8) through a transfer line (7). In the second reactor (8),polymerization was performed at 16.0 kg/cm².G and 60° C. In order toproduce a copolymer, ethylene was supplied to the second reactor (8) ata rate of 4.8 kg/hr without supply of catalysts. By use of a compressor(12), the pressure of a circulation gas was raised to 19.7 kg/cm².G. Afirst heat exchanger (13) was controlled so as to adjust the temperaturein a first separator (15) to −20° C. In this Example, gas was notdischarged through a gas discharge line (14). In the firstpolymerization reactor (6), the mole fraction of hydrogen was 9.0%, andin the second polymerization reactor (8), the mole fractions of hydrogenand ethylene were 8.4% and 40.0%, respectively. Through this two-stagepolymerization, a propylene-ethylene copolymer containing 45% ethylenein the copolymerization portion was produced at a rate of 35.3 kg/hr inthe second polymerization reactor. In the produced copolymer, limitingviscosity (η) of the homopolymerization portion was 1.1 dl/g and that ofthe copolymerization portion was 2.5 dl/g. In this Example, regardlessof no hydrogen being supplied to the second polymerization reactor (8),the concentration of hydrogen in the second reactor (8) was higher ascompared with the cases in Examples 1 and 2, due to the effect of theconcentration of hydrogen in the first polymerization reactor (6).

[0082] The results are shown in Table 1. TABLE 1 Comparative Example 1Example 2 Example 1 Concentration of  8.9  9.0  9.0 hydrogen in a firstpolymerization reactor (mol %) Concentration of  2.0  1.3  8.4 hydrogenin a second polymerization reactor (mol %) Concentration of 40.1 40.040.0 ethylene in a second polymerization reactor (mol %) Producedpolymer: 1.1/4.5 1.1/5.1 1.1/2.5 η of homopolymerization portion/ η ofcopolymerization portion Concentration of 45.0 45.0 45.0 ethylene at thecopolymerization portion (mol %)

[0083] As described above, the present invention allows easy andconsistent adjustment of the composition of gas in a gas-phasepolymerization reactor, to thereby produce a polymer having an intendedmolecular weight distribution and composition ratio.

What is claimed is:
 1. A method for polymerizing olefins in successive,multiple stages by use of a plurality of polymerization reactorsdisposed in series comprising at least one gas-phase polymerizationreactor after a first reactor, which method comprises removing amulti-component gas from a gas-phase reactor and pressurizing and/orcooling the gas to thereby liquefy a portion of the gas; discharging atleast a portion of the removed gas; and returning the remaining gas andthe liquid to the gas-phase reactor.
 2. A method for polymerizingolefins in successive multi-stages by use of a plurality ofpolymerization reactors disposed in series comprising at least onegas-phase polymerization reactor after a first reactor, which methodcomprises removing a multi-component gas from a gas-phase reactor andpressurizing and/or cooling the gas to thereby liquefy a portion of thegas; returning the liquid to the gas-phase reactor; further pressurizingand/or cooling the remaining gas to thereby liquefy a portion of thegas; discharging at least a portion of the gas; and returning theremaining gas and the liquid to the gas-phase reactor.